Clarify boundaries. You need to make clear that you do not want him in your space, calling you or harassing you in any way and if he does you will call the police. If indeed he does not heed your drawing the line report him to the police. Mental illness is not an excuse for destructive or illegal behavior.

Be very careful. In socializing with people with mental disorders, esp ex-boy friends who won't let go, one needs to be extra careful to avoid tragic scenarios and additional stress.
Involvement of third party, in addition to therapist/counselor, trusted friend, family member, is crucial initial step in sending the message that you are seeking a permanent break and intent on getting a restraining order if needed.